1. Field of the Invention
The present invention generally relates to a dynamic pressure bearing having grooves for generating dynamic pressure on either its cylinder member or its shaft member and, more particularly, to a dynamic pressure bearing for an X-ray tube having a rotary anode wherein lubricant made of gallium or gallium alloy is used.
2. Description of the Prior Art
A dynamic pressure bearing of this type, which is disclosed in the Japanese Patent Application Laid-open Publication No. 60-97536, has a cylinder member for supporting a rotary anode of an X-ray tube, a shaft member accommodated in the cylinder member in a manner that a given clearance is formed therebetween, and grooves formed on an inner peripheral surface of the cylinder member and/or on an outer peripheral surface of the shaft member for generating dynamic pressure. The clearance between the cylinder member and the shaft member is filled with lubricant made of gallium or gallium alloy.
The reason for use of gallium or gallium alloy as lubricant is that the lubricant is required to resist severe conditions of vacuum and high temperatures in the clearance between the cylinder member and the shaft member.
It is important that the cylinder member and the shaft member, which always contact the lubricant, should be made of a metallic material having corrosion resistance against gallium and gallium alloy. In the above dynamic pressure bearing, tungsten (W) or tungsten alloy is used as a material for the cylinder member and the shaft member.
However, these metallic materials are not only expensive but also difficult to work or machine.